Unplayable lag Please help!!=[

Hi, this is my first time posting here...and I'm really stumped as to what the problem is...I have been playing starcraft 2 since the release date which was over a year ago....and I haven't had any problems...but recently while I am playing the FPS drops literally to 0 from 40-50 fps and then pops back up and then drops again...I have no idea what is wrong....I have searched over and over on forums and whatnot...but no one seems to know what the problem is....I replaced my old graphics card lately with a Radeon HD 6950 and also i bought some new G Skill ram specifically my system is :
Windows Xp Service pack 3
Pentium(R) Dual-Core CPU E5400 @2.70 GHz
G.SKILL F2-6400PC2-6400 4GB 2X2GB DDR2-800 Ram
Radeon HD 6950 Graphics Card

I have also checked my temperatures
http://i41.tinypic.com/24uwy8m.jpg
It seems to me everything is quite normal...

I've also installed the new drivers to my graphics card, direct X 11 recently...and Avast Antivirus...I've ran ad aware, spybot, and Avast and eliminated all the spyware/ viruses....I've actually also tried Formatting my computer but to no avail...Is there something wrong with my system? I really need help.....please and thanks in advance=]

Any help will be greatly appreciated!!!!

Oh yea...Although I don't think this would be the problem...I thought it might be useful the requires for starcraft 2:

PC Minimum System Requirements*:

Windows® XP/Windows Vista®/Windows® 7 (Updated with the latest Service Packs) with DirectX® 9.0c
2.6 GHz Pentium® IV or equivalent AMD Athlon® processor
128 MB PCIe NVIDIA® GeForce® 6600 GT or ATI Radeon® 9800 PRO video card or better
12 GB available HD space
1 GB RAM (1.5 GB required for Windows Vista®/Windows® 7 users)
DVD-ROM drive
Broadband Internet connection
1024X720 minimum display resolution

PC Recommended Specifications:

Windows Vista®/Windows® 7
Dual Core 2.4Ghz Processor
2 GB RAM
512 MB NVIDIA® GeForce® 8800 GTX or ATI Radeon® HD 3870 or better

I'm pretty sure that CPU of yours is bottlenecking that GPU, so that may explain the stuttering issue.
Also, Starcraft 2 is pretty CPU dependent, so that's a reason for the sudden drop in FPS.
The temps look okay.

Does any other game show the same problem?

ALSO: You can't get DX11 unless you're running Windows Vista/7.

what is your PSU rated for? when you upgraded your GPU did you check that your PSU meets the requirements?

Also, your mobo seems to be logging some CPUTIN at 116C max, I'm not sure what that is (maybe lifetime total) but that's pretty darn high...

Actually I figured out the problem...lol I uninstalled my old gpu driver and reinstalled the new one and it works perfectly fine now haha!! thanks for the input!!

no i did update the new drivers....but i didn't remove the old ones so they interfered with the new ones lol